Integrated circuits are tested by probing their contact pads and observing the results on special test equipment electrically connected to the probes and designed for this purpose. Various types of probes have been used, ranging from individual probes held in automated probe positioning devices, to multiple probes arranged in a pattern matching that of the integrated circuit contact pads and arranged to make temporary contact. For example, one arrangement for testing integrated circuits with multiple probes is described in U.S. Pat. No. 4,975,638 issued Dec. 4, 1990 to Evans et al., in which a contactor sheet of flexible film material has probe contacts formed on the under surface thereof in a pattern matching the contact pads on the integrated circuit device, whereby when the IC device is moved so that its contact pads engage the probe contacts, this action causes the probe contacts to scrub the contact pads to ensure effective electrical contact.
Another multiple probe assembly for testing integrated circuits is disclosed in U.S. Pat. No. 5,416,429 issued May 16, 1995 in the name of McQuade et al. and assigned to the present assignee. In this patent, a flexible laminated member held in cantilever support fashion included individual probe fingers making direct contact with the integrated circuit contact pads. The laminated member was constructed of two beryllium copper plies adhered by a dielectric adhesive comprising a modified acrylic to provide impedance matching.
As the number and density of connection pads increase on integrated circuits, special multiple probe devices have been devised for holding the probes in a predetermined pattern corresponding to the integrated circuit to be tested, and slidably supporting the probes, which are constructed as vertical pins. The test device is moved against the bottom ends of the pins while contact is maintained with the exposed upper heads of the pins. The type of probe head thus constructed was developed by IBM and is described in a number of U.S. Patents including, for example, U.S. Pat. No. 3,806,801 describing an earlier construction. This type of probe holder, which is sometimes referred to as a vertical-pin integrated circuit probing device has been improved by IBM and other manufacturers. Such a device is manufactured and sold by applicant's assignee as a COBRA.RTM. probe. A vertical pin probing device is used in conjunction with a printed circuit test board, which is connected in test circuit relationship with the external test equipment for testing the integrated circuit.
Inasmuch as the matrix or pattern of exposed heads of the vertical-pin probes is relatively small and dense, and must be connected to a larger pattern of traces (PCB traces) on the printed circuit test board, an interconnection device commonly known as a "space transformer" is generally employed. Various types of space transformers are shown in the prior art, for example in U.S. Pat. No. 4,038,599 issued Jul. 26, 1977 to Bove et al., U.S. Pat. No. 3,654,585 issued Apr. 4, 1972 to Wickersham, U.S. Pat. No. 3,911,361 issued Oct. 7, 1975 to Bove et al., and U.S. Pat. No. 4,901,013 issued Feb. 13, 1990 to Benedetto et al. A common type of prior art space transformer comprises a wired interface as depicted in FIGS. 1 and 2 of the present application. The wired interface space transformer conducts each individual lead from a contact pad on the lower surface of the space transformer to a PCB trace. The mass of individual wires are then potted in epoxy to hold them in place. Due to the method of construction, impedance matching of the connections between the PCB traces and the probe heads is not possible.
Another shortcoming of existing space transformers is the cost of manufacture, including, in the case of the wired interface type, the labor to accomplish the individual wiring. It would be desirable to provide a space transformer in which different trace patterns may be easily computerized and produced by a photo lithographic process. Also it would be desirable to have a space transformer in which the repetitive contact between the space transformer and the heads of the vertical pins does not wear out the contact pads on the space transformer, but rather transfers the majority of wear to the heads of the replaceable vertical pins.
Adjustability must be provided for the space transformer with respect to the printed circuit board in order to comply with dimensional specifications, such as how far the probe pin tips in the vertical-pin probe holder must be below the bottom plane of the printed circuit board.
Accordingly, one object of the present invention is to provide an improved interconnection device for connecting a vertical-pin integrated circuit probing device to external integrated circuit test equipment.
Another object of the invention is to provide an improved impedance-matched space transformer for connecting a vertical-pin integrated circuit probing device to a printed circuit board.
Still another object of the invention is to provide an improved space transformer of laminated construction which simplifies impedance-matching, adjustability for alignment, and improved connection to the printed circuit test board.